Conventional EMLs comprise a distributed feedback laser (DFB) region, an isolation region and an EAM region. The EML is monolithically fabricated such that each region of the EML can be formed on a single substrate through a sequence of epitaxial growth processes. One of the layers of EML device comprises an active region layer. This layer includes a quantum well layer, and more commonly, includes multiple quantum well layers separated by alternating barrier layers. The bandgap of the quantum wells in the DFB region is such that the active region layer emits photons when a certain bias voltage is applied across the DFB. The bandgap of the quantum wells in the EAM region is also selected such that the quantum well layer absorbs photons that are emitted from the DFB region of the EML when a first bias voltage is applied across the EAM region, but allows photons to pass through when a second bias voltage is applied across the EAM region. The isolation region separates the DFB and EAM regions such that the DFB and EAM regions are electrically isolated from one another.
FIG. 1 illustrates a conventional modulated laser 100 comprising light emission region 110, isolation region 120 and modulator region 130. Manufacturing modulated laser 100 may include forming lower semiconductive buffer layer 150 on a substrate 140, forming active region layer 160 on or above the lower semiconductive buffer layer 150, forming upper semiconductive buffer layer 170 on or above active region layer 160, forming contact layer 180a-b on or above upper semiconductive buffer layer 170, and forming isolation layer 190 on or over the active region layer 160 and upper semiconductive buffer layer 170 in isolation region 120 separating the light emission region 110 and modulation region 130.
In high power EML applications, an appreciable amount of energy is generated by the absorption of photons in the EAM region. A relatively greater amount of this energy is dissipated in the portion of the EAM active region closest to the isolation region (i.e., where photons emitted from the light emission region are first incident), in comparison to the portions of the EAM active region farther away from the isolation region. This comparatively greater amount of power dissipation in the closer portion of the EAM region results in a temperature increase that causes a shift in the bandgap energy of the quantum wells in that portion, and the generation of sub-regions of varying bandgap energies during “steady state” operation of the EML. Consequently, the relatively close portion of the EAM region absorbs photons at an inconsistent rate when a constant voltage is being applied to the entire EAM active region.
This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.